Does Hemoglobin C Trait Affect A1c Test Results?

Yes, having the Hemoglobin C trait can interfere with standard A1c test results, making them appear falsely higher or lower than your actual blood sugar levels ^[1][2][3]. Whether the result reads too high or too low does not bounce around randomly; it depends entirely on the specific laboratory machine used to analyze your blood ^[2][4]. This happens because the physical structure of Hemoglobin C differs slightly from standard hemoglobin, which can confuse certain testing equipment ^[3][5].

Why the Interference Happens

Your A1c test measures glycated hemoglobin, which is the percentage of your red blood cells that have sugar attached to them ^[3]. This provides an average of your blood sugar levels over the past two to three months.

Hemoglobin C has a slightly different electrical charge than standard hemoglobin (Hemoglobin A) due to a minor genetic variation ^[3][1]. This charge difference does not affect how sugar attaches to your blood cells ^[5]. However, one of the most common laboratory methods for measuring A1c—called ion-exchange HPLC—separates hemoglobin based on its electrical charge ^[2][6]. When the machine encounters the altered charge of Hemoglobin C, it can struggle to tell the hemoglobins apart ^[6][7]. This overlap can result in a falsely high or falsely low A1c reading ^[6][3].

When you carry one gene for Hemoglobin C (the trait), your red blood cells usually have a normal lifespan ^[8][9]. This means the interference is purely a laboratory machine error ^[3]. (Note: If you have Hemoglobin C disease—carrying two genes—or HbSC, your red blood cells may break down faster than normal. A shortened cell lifespan will also falsely lower your A1c, regardless of the lab machine used ^[10]).

Reliable Testing Alternatives

If you have the Hemoglobin C trait, standard A1c testing is not necessarily off the table, but your doctor and laboratory must use methods that are not impacted by hemoglobin variants ^[11][4]. The National Glycohemoglobin Standardization Program (NGSP) maintains a publicly available website showing exactly which commercial A1c tests are affected by Hemoglobin C ^[2].

Fortunately, modern labs have several reliable options if standard methods fail:

• Boronate affinity chromatography: This specific type of A1c test measures the sugar directly attached to the hemoglobin, rather than sorting the cells by their electrical charge ^[6][12]. It is generally unaffected by the Hemoglobin C trait ^[4][2].
• Immunoassays and Enzymatic assays: These lab methods use antibodies or enzymes to identify glycated hemoglobin ^[2][11]. They are generally much less susceptible to interference, though rare exceptions exist, so the lab still needs to verify their specific equipment’s compatibility ^[13].
• Fructosamine testing: Instead of measuring sugar on hemoglobin, a fructosamine test measures sugar attached to other proteins in your blood ^[14][10]. Because it does not rely on red blood cells, it completely bypasses the hemoglobin variant issue ^[15][14]. It provides a blood sugar average over the past 2 to 3 weeks ^[16].
• Glycated albumin (GA) testing: Similar to fructosamine, this test measures sugar attached to albumin (a blood protein) and is not affected by hemoglobin variants ^[14][16].
• Standard Blood Glucose Tests: Simple fasting blood tests or finger-prick tests measure glucose directly in the blood plasma ^[17]. They do not rely on red blood cells and are completely unaffected by the Hemoglobin C trait ^[1].
• Continuous Glucose Monitoring (CGM): Using a wearable sensor to track real-time blood sugar is an effective way to monitor diabetes without relying on A1c tests ^[1][17].

Taking Action

Because many people with the Hemoglobin C trait have no symptoms, doctors and laboratories may not automatically know you carry it. During a routine annual physical, a falsely high A1c due to this interference could lead to a mistaken diagnosis of prediabetes or diabetes ^[1][2].

If you do not have diabetes, remind your doctor of your trait before any routine blood work so they do not misinterpret a flawed A1c ^[1]. If you do have diabetes and your A1c results ever seem disconnected from your daily at-home blood sugar readings, the Hemoglobin C trait may be causing laboratory interference ^[1][14].

You can advocate for yourself by using a simple script with your doctor or the phlebotomist:
“I have the Hemoglobin C trait. If we are running an A1c test, please note my trait on the lab order so they use a compatible testing method, or let’s use a fructosamine test instead.”

Your doctor can request that the lab use an alternative method or switch to alternative tests to ensure your general healthcare or diabetes care remains accurate ^[14][2][4].